1. Field of the Invention
The present invention relates to a power on/off circuit apparatus, which can turn on/off a power supply from an external power source to each electronic device based on an operation input of power switch, in electronic devices including a microcomputer.
2. Description of the Related Art
Conventionally, in electronic devices such as a DVD (digital video disc) player, a DVD-ROM (digital video disc-read only memory) drive and the like, when these devices are connected to an AC (alternating current) power source, a power is always supplied to a microcomputer. The microcomputer carries out a key scan sensing operation of a key matrix on which various input keys including a power switch are arranged, and then, makes an on/off control of power supply to individual electronic components when the power switch is operated.
Moreover, even when the power supplied to individual electronic components is turned off, the microcomputer is operating; in other words, these electronic components are operating in a power saving mode (key scan sensing operation is still continuing).
By the way, when the microcomputer hangs up due to any factors, key scan sensing operation is impossible, and even when the power switch is operated, the power of the these components is not turned off. For this reason, an AC code must be plugged out and in of a receptacle (plug socket) in order to cancel the above hang-up of the microcomputer.
In the case where the microcomputer makes a malfunction, there is a well-known technique of resetting the microcomputer without plugging the AC code out of the receptacle (e.g., refer to Japanese Unexamined Utility Model Publication No. SHO 57-204592).
However, according to the prior art disclosed in the above Publication, in the case where the microcomputer is reset by the power switch making a malfunction, the state of electronic components operating just before is lost; for this reason, a user must start the operation of electronic components at the beginning. Therefore, the user has a misunderstanding of making a power-on operation in spite of making a power-off operation from the power-on state by operating the power switch; as a result, the user has a strange feeling that something is wrong. Moreover, the electronic components are not operating in a power saving mode (key scan sensing operation is still continuing).